PITTSBURGH — Federal authorities are warning residents in the Pittsburgh area about a scam in which callers purport to be officials collecting fines from people who fail to report for jury duty. The U.S. Marshals Service on Tuesday said scammers are calling residents in the region pretending to be U.S. Marshals, court workers or others in law enforcement. Authorities say the callers say fines must be paid to avoid jail time. They also often ask people to call a number and provide their credit card information. Authorities say officials don’t call anyone to arrange payment of fines over the phone.